Continuous methods for scrubbing out hydrogen sulfide and ammonia from coke oven gas are known. The ammonia is scrubbed in the ammonia scrubber which is operated with water and arranged behind the hydrogen sulfide scrubber which is operated with aqueous ammonia and the ammonia is distilled in a distilling apparatus as gaseous vapors with a very low content of acid constituents. The ammonia is added to the upper part of the hydrogen sulfide scrubber in order to increase the ammonia concentration at this point, at which the gas entering the scrubber from the bottom has only a low content of hydrogen sulfide, with respect to the ammonia concentration. The reason for this is that this permits combining the hydrogen sulfide more extensively and more selectively with ammonia and removal of hydrogen sulfide from the gas. Such an increase of the ammonia concentration in the upper part of the scrubber is particularly desirable because the ammonia wash water circulating between the scrubber and the deacidifier is liberated in the deacidifier only up to 60 to 70% of acid constituents, particularly of hydrogen sulfide and carbon dioxide. The remaining portions return in a cycle to the scrubber and the ammonia combined with them is not available for scrubbing the hydrogen sulfide out of the gas. Only the content of free ammonia in the wash water is determinant for the removal of hydrogen sulfide. Without returning the gaseous ammonia vapors of the distilling apparatus to the scrubber, only about 80% of the hydrogen sulfide can be removed from the coke oven gas, while when the gaseous ammonia vapors of the distilling apparatus are fed to the scrubber, over 98% are scrubbed out so that a residual content of the order of 0.1 to 0.2 g H.sub.2 S/m.sup.3n remains therein.
From the foregoing considerations, it follows that the ammonia vapors fed to the hydrogen sulfide scrubber must themselves be very pure and possibly free of acid moieties like hydrogen sulfide and carbon dioxide as well as hydrocyanic acid. This is achieved by subjecting the ammonia wash water which frequently also contains coal water, to a particularly careful distillation in the ammonia still, conducting the vapors containing hydrogen sulfide, hydrogen cyanide and carbon dioxide into the deacidifier for the ammoniacal hydrogen sulfide wash water operated in combination with the ammonia still. The ammonia still, which is designed as a distillation column, is increased for the same purpose by several rectifying bottoms and equipped with additional cooling cycles. This method is expensive both in itself and as far as equipment is concerned. The method would be much more perfect if it were possible in a simpler manner to provide even purer ammonia vapors for introduction into the upper part of the hydrogen sulfide scrubber. Such a method is the basis of the present invention.